Riding mowers having a zero radius turn (ZRT) capability are well known in the mowing art. Such mowers have a frame that carries a power source, such as an internal combustion engine, for propelling the frame over the ground and for providing power for mowing. Two powered rear drive wheels are carried on the frame with the front of the frame having a pair of unpowered front wheels, the wheels collectively supporting the frame for rolling over the ground. Often, the unpowered front wheels are caster wheels.
The rear drive wheels in a ZRT mower are individually powered by separate hydraulic drive motors that receive pressurized hydraulic fluid from a hydraulic system driven by the power source of the mower. The drive motors are individually controlled by separate control levers placed adjacent an operator's seat provided on the mower frame. The mower is steered by advancing one lever farther than the other to cause one drive motor, and thus the drive wheel on one side of the mower, to rotate faster than the other drive motor and drive wheel, thereby causing the vehicle to turn. Very sharp spin or ZRT type turns can be accomplished by advancing one control lever forwardly while pulling the other control lever rearwardly to cause the drive wheels on the opposite sides of the mower to simultaneously rotate in opposite directions.
A rotary cutting deck is carried at the front of the mower. The cutting deck usually houses a plurality of cutting blades that rotate about substantially vertical axes to cut grass in horizontal cutting planes. The blades are typically staggered relative to one another with a center blade being offset forwardly of a pair of side blades located on either side of the center blade. This allows the orbits of the cutting blades to overlap without having the blades contact one another, thus avoiding the need for timing the rotation of the blades. As the mower is driven over the ground and the blades are rotated, the blades cut a relatively large unbroken swath of grass during each pass of the mower. Exmark Mfg. Co., Inc. manufactures and sells ZRT mowers of this type under its Lazer Z brand name.
To change the height of cut (HOC) of the grass, the cutting deck is vertically moved up and down relative to the mower frame and thus relative to the ground to change the height of the cutting blades relative to the ground. In many known mowers, the HOC system used to do this includes multiple suspension links to the cutting deck. These movable links move up and down simultaneously with one another under the action of a single control lever. The control lever has a plurality of discrete adjusted positions relative to the mower frame, often established by the control lever engaging against a pin, to allow the height of cut of the cutting deck to be adjusted in a plurality of discrete increments. The height of cut is adjusted by changing the location of the pin within an array of adjustment holes provided therefor on the mower frame. The pin is selectively inserted by the operator into whichever adjustment hole corresponds to the desired height of cut.
While the HOC system suspends the cutting deck from the mower frame, it is not the primary propulsion linkage to the frame. In mowers of this type, parallel struts have front ends pivotally connected to the rear of the cutting deck. The rear ends of the struts pivotally connect to some portion of the frame behind the cutting deck. The struts are generally horizontal. The purpose of the struts is to transmit propulsive force from the motion of the frame to the cutting deck, thus propelling the cutting deck forwardly and rearwardly as the mower frame moves forwardly and rearwardly. The struts are also desirably long enough to permit a wide range of vertical motion of the cutting deck, such as when the height of cut is adjusted over its maximum range of travel or the cutting deck floats relative to the mower frame during operation of the mower to adapt to ground contours.
In known mowers using a pair of parallel struts, the front ends of the struts are formed with a wide horizontal sleeve that is pivotally mounted to the deck on a pivot pin. The rear of the cutting deck has a forked mount that includes a pair of spaced mounting arms with the pivot pin extending through the mounting arms and the sleeve on the front end of the strut being received between the mounting arms. The use of a wide sleeve constrained between a pair of mounting arms provides lateral or side-to-side stabilization of the cutting deck. In other words, the interaction of the sleeve, pin, and mounting arms prevents the cutting deck from moving or swaying too much in a lateral or side-to-side direction.
However, this lateral stabilization structure is prone to wear due to the side loads involved. Over time, this structure wears and loosens up and begins to permit the deck to excessively sway or move from side-to-side. The structure can be rebuilt or repaired, but this is a disadvantage. It is also a disadvantage to simply continue to use the cutting deck with too much side-to-side motion as the quality of cut can be adversely affected.
Another disadvantage of prior art struts is the use of solid pivot pins to connect opposite ends of the struts to the deck and the frame. Such solid pivot pins transmit vibration and shock loads from the deck to the frame which can be felt by and affect the operator. For example, if the deck strikes an object, the shock load from the impact will be transmitted back through the struts to the frame and to the operator who is carried on a seat on the frame. In addition, the use of solid pins to connect the struts is relatively noisy as the struts pivot up and down on the pins during operation of the mower and as the pins move slightly in their supports as the deck shifts laterally during maneuvering. This noise can also be annoying to the operator or bystanders.
In addition, known strut designs are relatively difficult to assemble and require close tolerances. The front of each strut includes the aforementioned sleeve that is desirably closely received between the arms of the forked deck mount in order to provide sufficient lateral stabilization to the deck. However, it may be the case that after one strut is assembled in its forked mount, the placement of the front end of the other strut might be off when it comes to dropping it down between the arms of the other forked deck mount. Tolerances must be closely controlled to prevent this from happening and even then misalignment can still occur. This requires the parts to be moved or replaced in order to allow assembly to be completed, which is obviously a disadvantage.